Method of producing printing surfaces



March 8, 1960 1.. MAYR 2,927,858

METHOD OF PRODUCING PRINTING SURFACES Filed May 9, 1957 INVENTOR 1. upwe MA YR ATTORNEY United States PatentO 2,927,858 METHOD OF PRODUCINGPRINTING SURFACES- Imdwig;Mayr, Munich, Germany,assignor to WolfgangMuth, Munich-501b,. Bavaria, Germany Application May 9, 1 951, SerialNo.658,090 7 priority, application Germany May 11, 1956 1. Claim. (Cl. v96+35) fixed. material, are. carried. out. alternately and repeatedly.-

2,927,858 Patented 8 196i) M ICE (uj 'lreatingthe fixed photographmaterial with aqueous solutions or organic or inorganic acids. and/orsalts of such acids in'the presence of hydrogen peroxide,and

-(b-) Subsequently drying without intermediate hardening. g

The effect. of this procedure is, two-fold: the gelatine is loosened andmade adequately availablefor the buildup of printing elements-and inaddition excess gelatine is disintegrated. Informer processes thisexcess gelatine remained in the material due to the intermediatehardening operation and'the smaller printing elements were; urgedoutwardly of the surface resulting in the rapid wear of the-formedreliefblock as noted hereinbefore.

Accordinglyby the practice of the present invention it has becomepossible to influence the size of the printing elements and to, inaddition, obtain a coarsening or diminution of grain by the addition ofappropriate chemi In yet another process, the reproduction of an.objectis. made by exposure in a. camera on a gelatine-silver halidefilm, andthe. film is subsequently developed in a tanning developer. Thefilm is then partially dried, squeezed: face down on a. stable supportand subjected to a. washing in a warm; water: solution containing agentswhich retard. the swelling of the .gela-tine and which'preventfurtherphotographic development. This results in the establishment on.thestable support. ofbare and cov-. ered spots, the covered supportport-ions representing an image; of the. object in relief, the. coveredspots. being formed: with gelatine- Subsequently the gelatine. formingthe. image is hardenedzby' treatment withfa solution containingformaldehyde tannic acid and glycerine. .Such a process is described inU.S. Pate nt No. 2,532,390.

A major drawback of prior art processes however has been that duetoilrarderiing. of theravailable silver-free 'gelatinesuchgelatinecannot adequately contribute'to a suflicient buildup of theprintingel enaents which on their outer surfaces are ofsilverjconsequentlyalso such silver halide film' is exposed to lightunder a screen negative, light rays penetrate into the film to'dilterentdegrees of depth depending upon the intensity of the light and thetoning permeability of the negative. Depending upon toning value largeror smaller screen points are found to be distributed on and in thegelatine layer of the film; therefore the mass of silver-free gelatinebetween the screen elements is large or small.

In the process of chemical relief formation, on those areas where thereare many screen points and silver-free gelatine is thus present ingreater concentration, a greater expansion of the gelatine will takeplace. This silverfree expanded gelatine protrudes more or less from thefilm surface and if not sufiiciently reduced it will be attracted by thesilver of the screen points and will become molded. The small screenpoints then become elevated out of proportion, and in the case of a lineblock, for example, the printing element is worn out rapidly.

a The present invention contemplates the provision of a process whichovercomes the above noted drawbacks by providing for the disintegrationof the unhardened expanded gelatine to such an extent that the smallscreen elements do not protrude but are slightly depressed. This isachieved in the practice of the invention by:

of salts is utilized for optimum control.

cal compounds to the solution. For example, Farmer's Reducer maybeemployed for this purpose. 7

Reliefs produced in accordance with the principles of the presentinvention are immediately usablefor printing. The appropriate adjustmentof the temperature and makeup of the treating solution permits thedisintegration of silver-free gelatine tosuch extent that the smallprinting elements do not protrude but are slightly recessed as will benoted more particularly hereinafter.

The solution with which the fixed, unhardened photographic material istreated suitably contains an acid to provide'a pH below that of theisoelectric point of the gelatine. In addition a salt is included toprovide for controlled swelling of the gelatine and suitablya mixture Tofurther enhance pH control of the solution a buffer acid may beintroduced. The solution rate is materiallyaided in an. eflfectivecontrolled" manner by the hydrogen peroxide which functions in thevdisintegration of the gelatine Whil e numerous: modifications may bemade in the componentspf the bath, the temperatnrepf'thebath. and timeof .exposureto thebath, and whileruchwill. depend upon properties of thephotographic material such as film thickness, density and the like,conditions may be regulated to provide for the disintegration action ina desired manner and the functioning of the hydrogen peroxide.

The procedure of' the improved process is diagrammatically illustratedin the accompanying drawings wherein:

Figure 1 represents a positive printed through a cross line screen andfixed without hardening;

Figure 2 represents the positive of Figure stage in the swelling of thegelatine;

Figure 3 indicates the positive in a swollen condition; and

lat a first Figure 4 illustrates the processed photographic mate- Aceticacid grams 10 Sodium sulfate (crystalline) do Ferric sulfate(crystalline) do 30 Water cc 9.00

When the above ingredients have been thoroughly dissolved, the solutionmay be passed through a filter and 50 cc. of concentrated sulfuric acidis added to the clear solution while stirring well. The solution whichcontains the agents to induce gelatine swelling, is then'cooled to roomtemperature and reacted with about IO'grams of hydrogen peroxide. Theaddition of the hydrogen peroxide may suitably be in the solid-form,that is, in the form of tablets containing H and urea, for example. Thesolution thus prepared is preferably permitted to stand over nightbefore treating the photographic material.

A bath of the treating solution having a temperature of about 15' C. (59F.) is prepared and the photographic material bearing a positive imagecopied through the point screen (Figure 1) is immersed for aboutminutes. During the treatment the photographic mate rial may be lightlyrinsed in clear water. The immersion ence of the aqueous solutioncontaining a large amount of water the life will be longer.

In the described treatment the hydrogen peroxide functions to insure thedisintegration of the gelatine excess. The sulfuric acid and acetic acidprovide the pH ,at a potential below the isoelectric point toinsureswelling of the gelling-for this purpose other inorg'anic'andorganic acids,'including nitric, hydrochloric, phosphoric, may beemployed. The ionizable salts, ferric sulfate and sodium sulfate exertcontrol over the swelling; other trivalent and divalent ionizable saltsmaybe employed.

In general the ionizable salts and the acid "concentration forcombination with the hydrogen peroxide may be time will depend to someextent upon the thickness of the photographic material as well as thetoning value thereof-but in general an original thickness of 30 micronswill increase to about 100 microns. The swollen film (Figure 2) will inthe course of action raise the silver or screen elements (Figure 3); thegelatine in the areas of higher gelatine concentration will disintegrateto a greater degree however and the smaller screen elements in theproduct of the treatment will be somewhat recessed below the print plane(Figure 4).

The product of the treatment with the noted solution is rinsed well inclear water and dried in a circulating current of warm air. When dry theproduct is ready for printing. 7

If desired a solution of the agents which induce the swelling and whichcontain the peroxide may also include Farmers Reducer as referred tohercinbcfore. A suitable Farmers reducing solution is:

Ferricyanide stock solution (30%):

Potassium Ferricyanide oz 12 Water 07 28 Hypo stock solution: Sodiumthiosulphate Baum 35 It is to be noted that when the above two solutionsare combined they may lose their activity at room temperature in a shortperiod of time; however, in the presreadily selected to producecontrolled swelling and partial disintegration of the gelatine.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions and accordingly,it is desired to comprehend such modifications within this invention asmay fall within the scope of the appended claim.

/ I claim: 7

In a process of preparing a printing block from photographic filmcomprising a light-sensitive layer of silver halide gelatin emulsion andbearing a positive image thereon copied through a screen, developed andfixed so that the gelatin is substantially unhardened; the steps ofsubjecting the fixed and unhardened photographic film to an aqueousrelief forming solution to eifect swelling'of the gelatin substantiallywithout hardening the gelatin with said solution comprising 10 grams ofacetic acid, 90 grams of crystalline sodium sulfate, 30 grams of ferricsulfate, cc. of concentrated sulfuric acid, and about 10 grams ofhydrogen peroxide for every 900 cc. of water and the treatment beingeffective to swell and partially disintegratethe gelatin; rinsing thephotographic film in clear water; and subsequently drying thephotographic film without intermediate hardening of the gelatin therein.

References Cited in the file of this patent UNITED STATES PATENTS2,178,338 Frankenburger et al Oct. 31,v 1939 2,772,160 Hepher Nov.27,1956

